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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-03-09 08:05:43
  • Article ID: 670861

Cracking the Mystery of Perfect Efficiency: Investigating Superconductors

From the turn of the last century to today, scientists have explored why superconductors never lose current.

  • Credit: Image is taken from the Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006

    This figure shows how electrons pair up to cause superconductivity. Instead of traveling independently, the electrons couple into pairs that flow through metal without resistance.

  • Credit: Image is taken from the Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006

    In copper and iron-based superconductors, the spins on adjacent sites have north and south poles that alternate directions. Scientists think that the ordering of these magnetic poles may affect the electrons' interactions.

In 1911, physicist Heike Kamerlingh Onnes aimed to lower mercury’s temperature to as close to absolute zero as possible. He hoped to win a disagreement with Lord Kelvin, who thought metals would stop conducting electricity altogether at extremely low temperatures. Carefully manipulating a set of glass tubes, Kamerlingh Onnes and his team lowered the mercury’s temperature to 3 K (-454 F). Suddenly, the mercury conducted electricity with zero resistance. Kamerlingh Onnes had just discovered superconductivity.

This single finding led to a worldwide investigation that’s spanned a century. While it resolved one scientific debate, it created many more. The Department of Energy’s Office of Science and its predecessors have spent decades supporting scientists investigating the mystery of why superconductivity occurs under a variety of circumstances.

The answer to this question holds major opportunities for scientific and technological development. About six percent of all electricity distributed in the U.S. is lost in transmission and distribution. Because superconductors don’t lose current as they conduct electricity, they could enable ultra-efficient power grids and incredibly fast computer chips. Winding them into coils produces magnetic fields that could be used for highly-efficient generators and high-speed magnetic levitation trains. Unfortunately, technical challenges with both traditional and “high temperature” superconductors restrict their use.

“To the extent that Tesla and Edison introducing the use of electricity revolutionized our society, ambient superconductivity would revolutionize it once again,” said J.C. Séamus Davis, a physicist who works with the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center.

The How and Why of Superconductivity

Kamerlingh Onnes’ discovery set off a flurry of activity. Despite his grand visions, most of what scientists found only reinforced superconductors’ limitations.

One of the first big breakthroughs came nearly half a century after Kamerlingh Onnes’ initial finding. While most researchers thought superconductivity and magnetism couldn’t co-exist, Alexei A. Abrikosov proposed “Type II” superconductors that can tolerate magnetic fields in 1952. Abrikosov continued his research at DOE’s Argonne National Laboratory (ANL) and later won the Nobel Prize in Physics for his contributions.

The next big leap came in 1957, when John Bardeen, Leon Cooper, and John Robert Schrieffer proposed the first theory of why superconductivity occurs. Their theory, made possible by the support of DOE’s predecessor, the Atomic Energy Commission, also won them the Nobel Prize in physics.

Their theory contrasts how some metals work under normal conditions with how they act at extremely low temperatures. Normally, atoms are packed together in metals, forming regular lattices. Similar to the spokes and rods of Tinkertoys, the metals’ positively charged ions are bonded together. In contrast, negatively charged free electrons (electrons not tied to an ion) move independently through the lattice.

But at extremely low temperatures, the relationship between the electrons and the surrounding lattice changes. A common view is that the electrons’ negative charges weakly attract positive ions. Like someone tugging the middle of a rubber band, this weak attraction slightly pulls positive ions out of place in the lattice. Even though the original electron has already passed by, the now displaced positive ions then slightly attract other electrons. At near absolute zero, attraction from the positive ions causes electrons to follow the path of the ones in front of them. Instead of travelling independently, they couple into pairs. These pairs flow easily through metal without resistance, causing superconductivity.

Discovering All-New Superconductors

Unfortunately, all of the superconductors that scientists had found only functioned near absolute zero, the coldest theoretically possible temperature.

But in 1986, Georg Bednorz and K. Alex Müller at IBM discovered copper-based materials that become superconducting at 35 K (-396 F). Other scientists boosted these materials’ superconducting temperature to close to 150 K (-190 F), enabling researchers to use fairly common liquid nitrogen to cool them.

In the last decade, researchers in Japan and Germany discovered two more categories of high-temperature superconductors. Iron-based superconductors exist in similar conditions to copper-based ones, while hydrogen-based ones only exist at pressures more than a million times that of Earth’s atmosphere.

But interactions between the electron pairs and ions in the metal lattice that Bardeen, Cooper, and Schrieffer described couldn’t explain what was happening in copper and iron-based high temperature superconductors.

“We were thrown into a quandary,” said Peter Johnson, a physicist at Brookhaven National Laboratory (BNL) and director of its Center for Emergent Superconductivity. “These new materials challenged all of our existing ideas on where to look for new superconductors.”

In addition to being scientifically intriguing, this conundrum opened up a new realm of potential applications. Unfortunately, industry can only use “high-temperature” superconductors are for highly specialized applications. They are still too complex and expensive to use in everyday situations. However, figuring out what makes them different from traditional ones may be essential to developing superconductors that work at room temperature. Because they wouldn’t require cooling equipment and could be easier to work with, room temperature superconductors could be cheaper and more practical than those available today.

A Shared Characteristic

Several sets of experiments supported by the Office of Science are getting us closer to finding out what, if anything, high-temperature superconductors have in common. Evidence suggests that magnetic interactions between electrons may be essential to why high-temperature superconductivity occurs.

All electrons have a spin, creating two magnetic poles. As a result, electrons can act like tiny refrigerator magnets. Under normal conditions, these poles aren’t oriented in a particular way and don’t interact. However, copper and iron-based superconductors are different. In these materials, the spins on adjacent iron sites have north and south poles that alternate directions – oriented north, south, north, south and so on.

One project supported by the Center for Emergent Superconductivity examined how the ordering of these magnetic poles affected their interactions. Scientists theorized that because magnetic poles were already pointing in opposite directions, it would be easier than usual for electrons to pair up. To test this theory, they correlated both the strength of bonds between electrons (the strength of the electron pairs) and the direction of their magnetism. With this technique, they provided significant experimental evidence of the relationship between superconductivity and magnetic interactions.

Other experiments at a number of DOE’s national laboratories have further reinforced this theory. These observations met scientists’ expectations of what should occur if superconductivity and magnetism are connected.

Researchers at ANL observed an iron-based superconductor go through multiple phases before reaching a superconducting state. As scientists cooled the material, iron atoms went from a square structure to a rectangular one and then back to a square one. Along the way, there was a major change in the electrons’ magnetic poles. While they were originally random, they assumed a specific order right before reaching superconductivity.

At DOE’s Ames Laboratory, researchers found that adding or removing electrons from an iron-based superconducting material changed the direction in which electricity flowed more easily. Researchers at BNL observed that superconductivity and magnetism not only co-exist, but actually fluctuate together in a regular pattern.

Unfortunately, electron interactions’ complex nature makes it difficult to pinpoint exactly what role they play in superconductivity.

Research at BNL found that as scientists cooled an iron-based material, the electron spins’ directions and their relationship with each other changed rapidly. The electrons swapped partners right before the material became superconducting. Similarly, research at ANL has showed that electrons in iron-based superconductors produce “waves” of magnetism. Because some of the magnetic waves cancel each other out, only half of the atoms demonstrate magnetism at any one time.

These findings are providing new insight into why superconductors behave the way they do. Research has answered many questions about them, only to bring up new ones. While laboratories have come a long way from Kamerlingh Onnes’ hand-blown equipment, scientists continue to debate many aspects of these unique materials.

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Laser-Free Method of Ion Cooling Has Range of Potential Uses

Prof. Daniel Zajfman's universal ion trap cools to a tenth of a degree above absolute zero. The new method does not depend on the type or the weight of the ion and, thus, might be used to investigate the properties of large biological molecules or nanoparticles, among other things.

Tiny Lasers from a Gallery of Whispers

Whispering gallery mode resonators rely on a phenomenon similar to an effect observed in circular galleries, and the same phenomenon applies to light. When light is stored in ring-shaped or spherical active resonators, the waves superimpose in such a way that it can result in laser light. This week in APL Photonics, investigators report a new type of dye-doped WGM micro-laser that produces light with tunable wavelengths.

Copper Catalyst Yields High Efficiency CO2-to-Fuels Conversion

Berkeley Lab scientists have developed a new electrocatalyst that can directly convert carbon dioxide into multicarbon fuels and alcohols using record-low inputs of energy. The work is the latest in a round of studies coming out of Berkeley Lab tackling the challenge of a creating a clean chemical manufacturing system that can put carbon dioxide to good use.

Solar-to-Fuel System Recycles CO2 to Make Ethanol and Ethylene

Berkeley Lab scientists have harnessed the power of photosynthesis to convert carbon dioxide into fuels and alcohols at efficiencies far greater than plants. The achievement marks a significant advance in the effort to move toward sustainable sources of fuel.

New Evidence for Small, Short-Lived Drops of Early Universe Quark-Gluon Plasma?

UPTON, NY--Particles emerging from even the lowest energy collisions of small deuterons with large heavy nuclei at the Relativistic Heavy Ion Collider (RHIC)--a U.S. Department of Energy Office of Science User Facility for nuclear physics research at DOE's Brookhaven National Laboratory--exhibit behavior scientists associate with the formation of a soup of quarks and gluons, the fundamental building blocks of nearly all visible matter.

New Insights Into Nanocrystal Growth in Liquid

PNNL researchers have measured the forces that cause certain crystals to assemble, revealing competing factors that researchers might be able to control. The work has a variety of implications in both discovery and applied science. In addition to providing insights into the formation of minerals and semiconductor nanomaterials, it might also help scientists understand soil as it expands and contracts through wetting and drying cycles.

Discovery Could Reduce Nuclear Waste with Improved Method to Chemically Engineer Molecules

A new chemical principle discovered by scientists at Indiana University has the potential to revolutionize the creation of specially engineered molecules whose uses include the reduction of nuclear waste and the extraction of chemical pollutants from water and soil.

Biologist Reaches Into Electric Eel Tank, Comes Out with Equation to Measure Shocks

Vanderbilt University researcher Ken Catania stuck his arm into a tank with small electric eel 10 times -- the only way to get accurate measurements of the circuit created by animal, arm and water.

Fungi: Gene Activator Role Discovered

Specific modifications to fungi DNA may hold the secret to turning common plant degradation agents into biofuel producers.

New Study on Graphene-Wrapped Nanocrystals Makes Inroads Toward Next-Gen Fuel Cells

A new Berkeley Lab-led study provides insight into how an ultrathin coating can enhance the performance of graphene-wrapped nanocrystals for hydrogen storage applications.

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Wayne State Receives $1.2 Million NSF Grant to Develop Autonomous Battery Operating System

Researchers at Wayne State University led by Nathan Fisher, associate professor of computer science in the College of Engineering, received a $1.2 million grant from the National Science Foundation to address the need for effective, integrative battery operating systems that provide sustained and reliable power.

UAH leads effort that secures $20 million grant from the National Science Foundation

A partnership comprising nine universities in Alabama, including The University of Alabama in Huntsville (UAH) as the lead institution, has been awarded a $20 million, five-year grant by the National Science Foundation's Experimental Program to Stimulate Competitive Research (EPSCoR).

Sandia Labs Wins 5 Regional Technology Transfer Awards

Sandia National Laboratories won five awards from the 2017 Federal Laboratory Consortium for its work to develop and commercialize innovative technologies.

Tulane Receives Grant to Reduce Auto Emissions

Members of Tulane University's Shantz Lab will work with industrial scientists to assist in the development of next-generation materials designed to reduce harmful automotive emissions. The three-year old lab and its group of students have received a grant and equipment resources from SACHEM, Inc., a chemical science company.

Lab Leads New Effort in Materials Development

Lawrence Livermore National Lab will be part of a multi-lab effort to apply high-performance computing to US-based industry's discovery, design, and development of materials for severe environments under a new initiative announced by the Department of Energy (DOE) on Sept. 19.

ORNL Innovation Crossroads Program Opens Second Round of Energy Entrepreneurial Fellowships

Entrepreneurs are invited to apply for the second round of Oak Ridge National Laboratory's Innovation Crossroads program.

Los Alamos Recognized as Top Diversity Employer

For the second straight year, Los Alamos National Laboratory was recognized as a top diversity employer by LATINA Style and STEM Workforce Diversity magazine.

SLAC-Led Project Will Use Artificial Intelligence to Prevent or Minimize Electric Grid Failures

A project led by the Department of Energy's SLAC National Accelerator Laboratory will combine artificial intelligence with massive amounts of data and industry experience from a dozen U.S. partners to identify places where the electric grid is vulnerable to disruption, reinforce those spots in advance and recover faster when failures do occur.

Chaudhuri named Director of Manufacturing Science and Engineering at Argonne National Laboratory

Argonne National Laboratory announces the appointment of Santanu Chaudhuri, Ph.D., as the Director of the Laboratory's new Manufacturing Science and Engineering initiative, effective Sept. 14, 2017

Boise State Researchers Earn Grants to Manufacture Sensors for Nuclear Reactors, Space

National grants will be used to purchase advanced manufacturing equipment needed to build sensors suitable for extreme environments.

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Fungi: Gene Activator Role Discovered

Specific modifications to fungi DNA may hold the secret to turning common plant degradation agents into biofuel producers.

First Look at a Living Cell Membrane

Neutrons provide the solution to nanoscale examination of living cell membrane and confirm the existence of lipid rafts.

High Yield Biomass Conversion Strategy Ready for Commercialization

Researchers convert 80 percent of biomass into high-value products with strategy that's ready for commercialization.

Consequences of Drought Stress on Biofuels

Switchgrass cultivated during a year of severe drought inhibited microbial fermentation and resulting biofuel production.

Clay Minerals and Metal Oxides Change How Uranium Travels Through Sediments

Montmorillonite clays prevent uranium from precipitating from liquids, letting it travel with groundwater.

Tundra Loses Carbon with Rapid Permafrost Thaw

Seven-year-study shows plant growth does not sustainably balance carbon losses from solar warming and permafrost thaw.

Crystals Grow by Twisting, Aligning and Snapping Together

Van der Waals force, which that enables tiny crystals to grow, could be used to design new materials.

Vitamin B12 Fuels Microbial Growth

Scarce compound, vitamin B12, is key for cellular metabolism and may help shape microbial communities that affect environmental cycles and bioenergy production.

Carbon in Floodplain Unlikely to Cycle into the Atmosphere

Microbes leave a large fraction of carbon in anoxic sediments untouched, a key finding for understanding how watersheds influence Earth's ecosystem.

Bacterial Cell Wall Changes Produce More Fatty Molecules

New strategy greatly increases the production and secretion of biofuel building block lipids in bacteria able to grow at industrial scales.


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College Presidents Flock to D.C., Urge Senate to Pass Clean Energy Bill

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